The polymerization of epoxides such as propylene oxide or mixtures of propylene oxide and ethylene oxide using water and/or alcohols as initiators is of great industrial importance since the resulting polyether alcohols or polyether polyols are very versatile compounds which can be used as such or as intermediates in the manufacture of various products such as (flexible) polyurethanes, detergents, oil additives and brake fluids.
The polymerization of epoxides is normally carried out under basic conditions, e.g., by using potassium hydroxide or sodium hydroxide as a catalyst. Although products (polyether polyols or polyether alcohols) of good quality can be obtained, the use of these inorganic bases limits the capacity of the process since a long batch time is required to warrant good quality products. Shortening of the batch time is not impossible but it has the intrinsic disadvantage that the selectivity of the process is decreased substantially which seriously affects the product properties.
Therefore, alternative catalytic systems, allowing in principle a shorter batch time, have been suggested. Reference is made to double metal cyanide complexes such as disclosed in British Pat. No. 1,149,726 (for instance zinc hexacyanometallate-complexes further containing zinc chloride, water and an organic ligand) and in East German Pat. No. 148,957 (specifically metal hexacyano iridium complexes further containing chloride, water and an ether).
As the preparation of such double metal cyanide complexes is rather complicated and tedious, in copending application Ser. No. 475,018, filed Mar. 14, 1983, a novel class of double metal cyanide complexes is described and claimed, which catalysts can be prepared without any of the major handling problems normally encountered in the preparation of double metal cyanide complexes. Moreover, this class of novel double metal cyanide complexes appears to be stable, both as such and in admixture with the appropriate initiator. The catalytic activity of these novel double metal cyanide complexes is at least on a par with the activity of the double metal cyanide catalysts known in the art. Although the yields, expressed in kg polyether polyol or polyether alcohol/g catalyst are reasonable, any improvement in the yield is still highly desirable since this would contribute substantially to the feasibility of the polymerization process.
It has now surprisingly been found that the presence of certain promoters as defined hereinafter, has a very beneficial influence on the yields of polyether polyols prepared using catalysts based on double metal cyanide complexes. Yield increases as high as 100% or even higher can be obtained under otherwise identical reaction conditions.